In extra-vehicular activity (EVA) pressure suit design, it is desirable to properly position a subject with respect to the pressure suit. The suit typically includes bearings that enable sections of the suit to rotate relative to one another. One such bearing is a scye bearing that is provided in each shoulder area of the suit. Proper positioning of the suit relative to the subject is needed to achieve and maintain alignment of subject's joints with the suit's joints for effective mobility and efficient performance of EVA tasks. An inherent conflict exists between this need and the requirement for significant clearance between the suit and body to allow a practical donning process.
Typical NASA design concepts for planetary exploration spacesuits use a rear entry system in which the crew enters the suit through a hatch in the back of a hard (or partially hard) upper torso (HUT). Rear entry spacesuits have a traditional donning problem. For use, the shoulder holes need to be on the sides. With both a hard upper torso and a pressurized soft upper torso, the shoulder holes are typically fixed in one position.
Chest breadth varies from subject to subject. This makes optimal fit from even a limited number of upper torso sizes almost impossible. To further complicate fit, U.S. space programs traditionally carry the conflicting goals of supporting 5th percentile Asian female to 95th percentile American male subjects yet desiring a minimum inventory of suit sizes or modules.
In the 1960s Hamilton Standard designed and made a mobility suit that was quite flexible through the subject's range of motion. The suit was soft and did not utilize scye bearings. A cord restraint system was provided in the shoulder areas that allowed the shoulder and upper arm to move in any direction or position to be anthropomorphically compliant while pressurized. During that period, Hamilton Standard developed a non-flexing when pressurized cord sizing adjustment system for pressure suit limbs. In this system, areas could be lengthened or shortened by pulling in or letting out the cord.